1. Field of the Invention
This invention relates generally to a regulator spool valve controlled by a direct acting solenoid with a multiplex latch valve and located in a machined main control casting of an automatic transmission.
2. Description of the Prior Art
An automatic transmission includes a hydraulic system for regulating fluid pressure and hydraulic fluid flow in various lines connected to components of the transmission. The system includes a regulator spool valve packaged in a main control casting, which is machined at a transmission production plant. The casting, preferably of an aluminum alloy, is usually referred to as a valve body. The components of the system are assembled in the valve body and have transfer functions characterized at the plant.
A solenoid-actuated regulator valve controls pressure communicated from the valve to a clutch or brake whose state of engagement and disengagement determines the gear in which the transmission operates.
Transmissions clutch regulators require a method to provide hydraulic pressure to clutches and brakes for high torque operating conditions such that the required pressure can be delivered independently of the control pressure range suitable for shift control. The separation of static capacity (high torque) and dynamic control pressure ranges is accomplished through use of latch valves.
The typical latch valve acts to override the regulation of the clutch regulator by exhausting the feedback pressure at the spool. This causes the spool to no longer be in force equilibrium, resulting in spool traveling to its limit opening full communication between supply and control pressure ports. The exhaust of the feedback port and subsequent valve travel result in significant delay and undershoot in clutch control pressure on transition back to dynamic pressure control state.
A need exists in the industry for a latch valve formed in a valve body and operating with a regulating valve such that shift control of a transmission control element can be separated from the high pressure that is used to produce the high torque transmitting capacity of the control element when the element is engaged, which will eliminate deficiencies associated with altering regulator feedback pressure, and can be used in conjunction with self-contained devices such as direct acting solenoids.